The Relative Importance of Phenotypic Plasticity Versus Evolutionary Change in Predicting Historical Patterns of Maturation in Exploited Stocks

Much of the debate on the occurrence of fisheries-induced evolution has focused on the relative contributions of phenotypically plastic and evolutionary responses. Here we develop a multi-trait, stock-specific model for Northeast Arctic cod (Gadus morhua) to analyze the dynamics of fisheries-induced evolution when phenotypically plastic maturation and growth are accounted for. Specifically, we assess the levels of genetic variance in each of four quantitative life-history traits that provide the best match between model-predictions and 74 years of data on age and length at maturation. Revealing complex eco-evolutionary dynamics, our results predict that (1) fishing has caused an evolutionary response in Northeast Arctic cod that although small in magnitude, has nonetheless contributed to the observed decreases in age and length at maturation, (2) fishing-induced evolution, in particular towards increased growth rates, has prevented this stock from collapsing in the wake of elevated fishing pressures, while (3) the extent to which evolution is needed to explain the observed maturation trends varies among plausible alternative scenarios for density-dependent growth. We also show that although an evolutionary model outperforms a non-evolutionary model, the amount of evolution of traits is predicted to be smaller than suggested in previous studies.